Activities with three month old

My son is about to be three months old. I am home with him until he is about six months old. What kinds of activities do you do with your three month old to keep them entertained? We are about to extend time between naps and I’m worried about keeping him busy.

We do tummy time, singing, high contrast, and play with some toys. Just wondering if I’m missing anything I could or should be doing with him.